When moving objects short or long distances, that is commonly "object transportation" in its modern form there are demands for identification of the objects in question. These may be individual objects, pallets with objects, boxes or containers or other. The identification is important when considering efficiency or safety.
There is therefore a need for a system for reading data from the objects present in object transportation. Usually, these data are required to be forwarded to some superior system or centre. In certain cases it is desired to refer information to the objects from this centre, for example with the purpose to limit the demands on the geographical covering of the centre.
There are other areas, where there is a need to forward information from data carrying objects to a more or less distant centre, for example in connection with rental cars. Also human objects, that is persons, such as sportsmen on check-ups or persons for which safety check-ups are needed can be provided with data carriers, from which information can be transmitted to such a centre.
Hitherto it has proven difficult to achieve efficient systems of this kind. One suggestion has implied that the objects in question were provided with an optic code, for example a bar code, which was read with a manually carried reading pistol that was connected to a radio transmitter for communication with the superior system, that is the centre. Quite extensive apparatus is required for the purpose, as separate media are used for communication with the object, or rather the data carrying device on it, and communication with the centre. In practice, different physical units must be used for the optic reading and radio transmission, respectively. It is difficult to get general frequency permission for radio transmission, since different radio bands are allowed in different countries. Furthermore, communication at radio frequency does not admit compact directed antennae, which leads to high demands on transmitted effect and problems with interferences between different equipment.
Another proposed system for the transmission of information from objects to a centre is presented in PCT/US91/05234. Here, a communication unit is used to communicate, on one hand with a number of objects of different kinds, all provided with small radio transmitters, and on the other hand with a centre. In the first case FM radio waves of relatively low effect are used and in the second case FM radio waves of relatively high effect are used. The communication unit is provided with a memory. Such a system shows the same disadvantages as the one just mentioned, but is still more expensive, because every object must be provided with its own radio transmitter.
Moreover, none of the two mentioned systems admits that the information data on the objects are changed wirelessly.
A technique that has been used for a long time relates to so-called transponders, that is small units, which through radiation, especially with microwaves, are brought to emit a signal containing coded information. SE-364 677 with priority from 5 May 1970 describes identification of vehicles, equipped with transponders, which are activated through radiation with a microwave signal from a questioning station, that is a centre, which is rigidly mounted.
Transponders of this kind are also described in SE-750 3620 and SE-760 9732. The latter of these patents relates to an embodiment of a central unit and transponder, which admits that data are transmitted also from the central unit to the transponder.
Transponders can contain relatively great amounts of information, but they can only be read at a relatively short distance, in the order of a few meters. They are consequently not usable for the identification of goods in various situations, for example on a loading platform or airport, where difficulties are encountered with bringing the objects within reading distance from a central unit.